PAA-Functionalized UiO-66 Incorporated into Lotus Biochar-Chitosan Hydrogel: A Bimetallic Adsorbent with Enhanced Adsorption Capacity for Antibiotics

To address the persistent challenge of antibiotic contamination in aquatic systems, we developed a novel bimetallic hydrogel composite, i.e., Co/Zn-UiO-66-PAA/chitosan @biochar (Co/Zn-UPCB) through strategic integration of polyacrylic acid (PAA)-functionalized metal organic frameworks (UiO-66), lotus leaf-derived biochar, and natural chitosan. This hierarchically porous architecture synergistically combines chemical functionality (abundant carboxyl/amino groups), structural stability (3D crosslinked network), and bimetallic active sites (Co²⁺/Zn²⁺), exhibiting remarkable adsorption capacities of 1693.45   mg/g for tetracycline (TC)   at pH of 7 and 1201.63   mg/g for ofloxacin (OFL)   at pH of 5. Additionally, kinetic and isotherm studies reveal distinct removal pathways. TC adsorption follows chemisorption-dominated monolayer binding via coordination and hydrogen bonding, while OFL removal occurs through physisorption-driven electrostatic interactions. The Co/Zn-UPCB composite maintains near 80% efficiency after ten regeneration cycles and demonstrates strong anti-interference capability against common coexisting ions (except Ca²⁺). This work provides a sustainable design leveraging waste-derived biochar and biopolymer for efficient adsorption of TC/OFL, enabling precision water remediation.